Industrially manufactured products are often subjected to thermal treatment with the aid or heaters. Even small deviations in the thermal process can lead in such cases to an enormous adverse effect on the product quality. In order to increase the quality of a heat-treated product it is important to be able to focus the energy needed very precisely in terms of time and space. This is done with the aid of specific heating controllers and/or regulators, which guarantee a highly precise activation of heating elements. In such cases resistive loads in the form of radiant heaters, especially infrared radiant heaters, are frequently used as heating elements.
For example blow molding systems usually have radiant heater arrays to heat preforms. The radiant heaters (radiant infrared heaters) are then frequently controlled/regulated and monitored in respect of their power output by a heating control and/or regulation device supplied with electricity via a switching element connected into the power supply.
To this end the heating control and/or regulation device mostly receives set values for the heating power of the connected heating elements via a communications system, such as an open field bus of a higher-ranking control and/or regulation device for example, e.g. of a stored program controller (SPC). The set values can be present for example in the form of absolute set values, set values related to a maximum power or set values related to a nominal power. The power can relate for example to a heating power to be output or to an electric power of heating elements to be consumed. Activation signals for the switching elements are then derived from these set values in the heating control and/or regulation device with the aid of a predetermined control and/or regulation algorithm. The set values can however also be present in the form of pulse packets or percentages of half waves per unit of time (e.g. per second), from which activation signals for the switching elements can then be derived directly. The switching states of the switching elements and thus heating powers of the heating elements are then controlled or regulated via the activation signals. For simplification and for better understanding all the set values are referred to below as “set values for a heating power”.
The switching elements can be activated and thus the switching state or the heating power can be controlled or regulated for example with a phase controller or a half wave controller with switching elements switching at zero power during the zero crossing. Semiconductor switches (e.g. solid-state relays) are used here as switching elements for example.
The temperature of a product to be heated is actually controlled or regulated in such cases in the higher-ranking control and/or regulation device, which has a corresponding control and/or regulation algorithm for this purpose.
To this end the higher-ranking control and/or regulation device is connected either directly or indirectly (via an input module) to a temperature measurement device for actual values of a temperature and is configured such that it detects the actual values of the temperature from this temperature measurement device and with the aid of the control and/or regulation algorithm creates set values for the heating power of the heating elements, which are then communicated by the communications system to the heating control and/or regulation device.
In a corresponding manner the higher-ranking control and/or regulation device can be connected either directly or indirectly (e.g. via analog or digital input modules) to current and/or voltage sensors for detecting additional current and/or voltage values, to analog or digital signal generators for detecting additional analog or digital signals and either directly or indirectly (e.g. via analog or digital output modules) to actuators.
The input and the output modules can in such cases be attached, as individual separate modules or grouped together in a separate module, to the heating control and/or regulation device and communicate the measured values and signals via the heating control and/or regulation device and its communication interface and via the communications system to the higher-ranking control and/or regulation device. As an alternative the input and the output modules can involve components entirely separated from the heating control and/or regulation device, each with their own communication interface to the communications system.